Recently, as growing for aspirations of ubiquitous ear, research for next generation electronic devices are being conducted globally and actively. According to acceleration of research on an organic display, an organic solar cell, and the like, importance to development of a transparent electrode material is raised so as to commercialize these devices. A transparent electrode for the next generation electronic devices should satisfy a mechanical flexibility, a superior optical property (light transmittance>85%, @550 nm), and a superior electrical property (sheet resistance<15Ω/□).
As disclosed in Korean Laid-Open Patent Application No. 2013-0027991 and the like, a transparent electrode being currently and widely used is an indium tin oxide (ITO) thin film in which an indium oxide is doped with a tin oxide. The ITO, however, has problems as follow.
(1) When an ITO transparent electrode is formed on a glass substrate, a high temperature thermal treatment over 300° C. is possible to obtain a crystalline ITO thin film having a low sheet resistance, or otherwise, when the ITO transparent electrode is formed on an organic substrate such as a polyethylene terephthalate (PET), a thermal treatment is performed below 200° C. so as to prevent a deformation or damage to an organic material such that there is a problem in which an amorphous ITO thin film having high sheet resistance is formed.
(2) Unlike a metal material and a polymeric material, an ITO transparent electrode is easily cracked due to a bending of a substrate to cause difficulty in application to devices
(3) Owing to an explosive increase of demanding for an ITO transparent electrode for use in a flat panel display, a mobile device, a touch panel, and the like, there are problems in which the cost of indium, which is a main raw material of the ITO transparent electrode, has steadily increased and cost competitiveness is weakened due to limited reserves.
(4) Upon formation of a thin film, a process condition requiring a high temperature and a high vacuum acts one reason to cause a cost increase of an ITO transparent electrode.
In order to substitute for an ITO transparent electrode and to obtain a flexible transparent electrode, a transparent electrode can be formed at a low temperature for enabling a manufacture of the transparent electrode on a flexible substrate while maintaining “flexibility” in addition to “high transmittance” and “low sheet resistance.” For developing a transparent electrode satisfying these conditions, researches across various fields including a conductive polymer, an oxide-metal-oxide (OMO) structure, a graphene, an ultra-thin metal film, and the like have actively conducted, but, up to this day, a transparent electrode satisfying all of mechanical, optical, and electrical properties has been not developed.